1. Field of the Invention
The present invention relates to a vertebra correcting and fixing device to be used for holding a vertebra in a desired spatial arrangement.
2. Description of Related Art
To correct vertebras, there has conventionally been conducted a correcting operation using a rod and three or more vertebra correcting and fixing devices each having a vertebra fixing screw. According to such a correcting operation, the vertebra fixing screws are threaded into the pedicles of vertebrae to connect the vertebra correcting and fixing devices to the vertebrae, and the vertebra correcting and fixing devices are joined to one another by the rod. Then, the rod is suitably deformed to fix the vertebrae in a desired arrangement.
As prior art, the U.S. Pat. No. 5,176,680 discloses a vertebra correcting and fixing device to be used in such a correcting operation. The arrangement of this Vertebra correcting and fixing device is shown in FIG. 4 in the present application. This vertebra correcting and fixing device 20 is arranged such that a rod B is attached into a vertebra fixing screw 22 provided at the top thereof with a U-shape seat portion 21. The device 20 comprises a clamping screw 23 and a split ring 24 threadedly connected to the upper side of the seat portion 21. With the rod B inserted into the split ring 24, the split ring 24 is fixed between the clamping screw 23 and a bottom surface 25 of the seat portion 21.
The split ring 24 is provided on the outer peripheral surface thereof with a spherical convex surface. When the clamping screw 23 is loosened, this outer peripheral surface can come in sliding contact with the bottom surface 25 of the seat portion 21. This enables the rod B to be adjusted in direction.
When the clamping screw 23 is fastened, the outer peripheral surface of the split ring 24 not only comes in contact with both a complementary spherical concave surface formed at the head (lower portion) of the clamping screw 23 and a complementary spherical concave surface formed in the inner wall surface of the seat portion 21 of the vertebra fixing screw 22, but also comes in pressure contact with the bottom surface 25 of the seat portion 21. This regulates the movement of the split ring 24 and also the movement of the rod B inserted thereinto.
When the split ring 24 is moved with the clamping screw 23 fastened, the rod B is changed in direction to loose the vertebra correcting effect. Therefore, the split ring 24 should securely be fixed with a large fixing force.
According to the arrangement of the prior art above-mentioned, however, the split ring 24 is merely held and fixed by the clamping screw 23 between the same and the bottom of the seat portion 21. Therefore, the split ring 24 fixing force is not sufficient. This involves the likelihood that the split ring 24 is moved when a large stress is exerted to the rod B even though the clamping screw 23 is fastened.
Further, according to the prior art above-mentioned, the clamping screw 23 can be fastened only in the axial direction of the vertebra fixing screw 22. Accordingly, if an obstacle is present in the axial direction of the vertebra fixing screw 22, this makes it difficult or impossible to fasten the clamping screw 23.
Further, according to the prior art above-mentioned, since the split ring 24 comes in contact with the bottom surface 25 of the seat portion 21, the movable range of the rod B is disadvantageously small. More specifically, when vertically rotating the rod B in the axial direction of the vertebra fixing screw 22, the inclination of the rod B at the time when the rod B comes in contact with the ridgeline of the bottom surface 25 of the seat portion 21, is relatively small.
It is a first object of the present invention to provide a vertebra correcting and fixing device in which the rod direction is adjustable and which can securely regulate the movement of the rod after the rod has been fixed.
It is a second object of the present invention to provide a vertebra correcting and fixing device in which, even when an obstacle is present in the axial direction of the vertebra fixing screw, the rod fixing operation can successfully be conducted while avoiding this obstacle.
It is a third object of the present invention to provide a vertebra correcting and fixing device in which the rod movable range is large, enabling the device to be applied to a greater number of cases.
According to the present invention, a vertebra correcting and fixing device comprises: a vertebra fixing screw to be threadedly connected to a vertebra; a movable spherical body which can be combined with the vertebra fixing screw; and a clamping screw threadedly connectable to the movable spherical body. The movable spherical body is substantially spherical, has a split through-hole formed in the diametrical direction thereof, and also has a screw hole extending at right angles to the split through-hole and communicating therewith. Provision is made such that the clamping screw is threadedly connected to this screw hole. The vertebra fixing screw is provided at one end thereof with a threaded portion and at the other end thereof with a groove-shape seat portion for receiving and holding the movable spherical body.
Preferably, the seat portion is capable of rotatably holding the spherical body.
According to the vertebra correcting and fixing device of the present invention, the split through-hole is preferably arranged such that a rod to be used for correcting a vertebra together with the device, can be inserted in the split through hole.
Preferably, the screw hole is arranged much that, when the clamping screw is fastened, the rod receives a pressing force from the clamping screw and is pushed to the inner wall surface of the split through hole in the movable spherical body, and that a pressing force from the rod causes the movable spherical body to receive force which tends to open and spread the slit of the split through-hole.
Preferably, the screw hole is formed in the spherical body at its position opposite to the slit of the split through-hole. Thus, a pressing force from the clamping screw can be transmitted to the rod, and a pressing force from the rod is exerted to the spherical body, causing the slit thereof to be spread or opened.
According to the present invention, when the clamping screw is fastened with the rod inserted into the split through-hole in the movable spherical body, the rod is pushed to the split through-hole for example at its bottom portion (at the split side). When the rod is moved to the narrower bottom portion of the split through-hole, the rod strongly pushes the wall surface of the bottom portion. Thus, the rod is fixed in the split through-hole in the movable spherical body, and the corresponding portions of the movable spherical body are pushed and spread outwardly. The portions thus spread of the movable spherical body are strongly pushed to the groove shape seat portion of the vertebra fixing screw. Accordingly, the reaction of the seat portion causes the movable spherical body to be securely fixed to the seat portion.
According to the vertebra correcting and fixing device of the present invention, the direction of the correcting rod can be adjusted and the direction once fixed can securely be maintained. This prevents the rod from being moved after the rod has been fixed. This eliminates the necessity of conducting an operation again, thus enhancing the satety.
Further, the spherical body to which the clamping screw is threadedly connected, is rotatable with respect to the seat portion of the vertebra fixing screw. This enables the screw hole to be turned in other direction than the axial direction of the vertebra fixing screw. It is therefore possible to select, out of a wide angular range, the working space for fastening the clamping screw. Accordingly, if there is an obstacle in the axial direction of the vertebra fixing screw, the clamping screw fastening working space can be assured in other direction than this axial direction. The clamping screw can therefore be fastened with good working efficiency. This enables the vertebra correcting and fixing device to be applied to a greater number of cases.
The seat portion may comprise a pair of opposing pieces which hold the spherical body thereby and therebetween. In this case, the end portion of the screw hole in the spherical body is preferably located as projecting from the two opposing pieces.
According to the arrangement above-mentioned, the opposing pieces are not an obstacle to the operation of fastening the clamping screw. Accordingly, the direction of the screw hole of the spherical body may be selected out of a wider angular range. This facilitates the clamping screw fastening operation.
Preferably, a gap is formed between the spherical body and the bottom surface of the seat portion. This increases the inclination of the rod at the time when the rod comes in contact with the ridgeline of the bottom surface of the seat portion when vertically rotating the rod in the groove-shape seat portion. This increases the movable range of the rod.
Preferably, the seat portion is provided at the bottom of the groove-shape thereof with a base portion, this base portion being provided at one or both ends of the groove-shape bottom with a spot-facing portion. According to such an arrangement, the rod vertical rotatable angular range can further be increased.
Preferably, the length of the spherical body along the split through-hole is shorter than its length along the direction at right angles to the split through-hole. Such an arrangement facilitates the assembling of the spherical body with the seat portion.
Preferably, the length of the spherical body along the split through-hole is shorter than the opening width of the groove-shape seat portion.
These and other features, objects, advantages and effects of the present invention will be more fully apparent from the following detailed description set forth below when taken in conjunction with the accompanying drawings.